The present invention concerns internal combustion engines of the type that include an electronically controlled hydraulic system for variable operation of the engine""s inlet valves.
In American patent U.S. Pat. No. 6,237,551, the Applicant has already proposed an engine including:
at least one inlet valve for each cylinder, equipped with respective elastic means of return that push the valve towards a closed position, for controlling the respective inlet port,
at least one camshaft for operating each inlet valve of the engine""s cylinders via the respective valve lifters, each inlet valve being controlled by a respective cam of said camshaft.
in which each of said valve lifters commands the respective inlet valve against the action of said elastic means of return via the interposition of hydraulic means including a pressurized fluid chamber,
the pressurized fluid chamber associated with each inlet valve being suitable for connection via a solenoid valve to a discharge channel, for the purposes of decoupling the valve from its respective valve lifter and provoking rapid closure of the valve under the effect of the elastic means of return, and
electronic means of control for controlling each solenoid valve for varying the time and opening travel of the respective inlet or exhaust valve according to one or more of the engine""s operating parameters.
In a multi-cylinder engine, the inlet ports of the engine""s cylinders are connected to an inlet manifold that receives air for feeding the engine. The operating cycles of each cylinder are obviously but of phase with respect to each other, in consequence of which the induction phases occur at different times. For a series of reasons, of which the different positioning of the cylinder inlet ports with respect to the inlet duct of the inlet manifold, uneven amounts of air can be sucked into the various cylinders of the engine.
The object of this invention is that of resolving this problem for an engine of the type indicated at the beginning.
In order to achieve this objective, the subject of the invention is an internal combustion multi-cylinder engine possessing all of the above indicated characteristics and also characterized in that the engine has an inlet manifold, connected to the various inlet ports of the engine""s cylinders, in which air-feed flow sensors are located, and in that said electronic means of control are capable of detecting the dispersion of air sucked into the various cylinders of the engine on the basis of an output signal from said sensors and for controlling the hydraulic system for actuating the inlet valves of the engine""s various cylinders in a differentiated manner, in order to reduce said dispersion to a minimum.
In the engine in accordance with the invention, the dispersion of air sucked into the various cylinders is detected via an airflow sensor located in the inlet duct upstream of the inlet manifold. The purpose of minimizing the dispersion is to try to make the amount of air sucked in by each cylinder reach the average value of air inducted during the engine cycle. As already indicated, dispersion minimization is implemented by control differentiation and, in particular, by the opening times of the inlet valves.
In a preferred form of embodiment, the estimate of the dispersion of inducted air in by each cylinder with respect to the average value is obtained by evaluating the difference between the estimate of air entering the cylinder, which is based on the output signal of said sensors, and a predetermined reference value that must be reached to achieve compensation of the dispersion.
Always in the case of the preferred form of embodiment, the estimate of inducted air is obtained by selecting the most significant sample from those related to the induction phase of the cylinder in question. In particular, the most significant sample is that relative to the maximum value of those related to the induction phase of the cylinder under consideration. The less the inlet duct is restricted by the engine""s butterfly valve, the more significant the sample is. In other words, notwithstanding the fact that the amount of air taken in by the engine can be achieved independently of the action of the butterfly valve thanks to the engine""s variable valve control system control, the estimate of air entering each cylinder with the herein described method is preferably taken with the butterfly valve completely open. The reference value to be reached that is used in the above-described method is determined in a preliminary, experimental phase. Possible faults and/or malfunctions of air-induction system components that have an impact on the air taken in by a single cylinder can be diagnosed via the real-time analysis of the dispersion of air inducted by the cylinders.